Cooperative Fish and Wildlife Research Units Program: Georgia
Education, Research and Technical Assistance for Managing Our Natural Resources

Lunar and tidal phases, along with bait type, were examined as potential sources of bias affecting catch rates of sub-adult sharks on hand-retrieved longlines in Georgia’s estuaries. Sampling occurred during April-September from 2001-2003 in eight of Georgia’s nine estuaries when the presence of sub-adult sharks is high. The effects of lunar and tidal phases on catch rates of sharks were evaluated during 2001 and 2002.The effect of bait type (i.e., squid Loligo spp. or spot Leiostomus xanthurus) on catch rates of sharks was evaluated during 2003. During 2001 and 2002, 420 sub-adult sharks, representing two families (Carcharhinidae and Sphyrnidae) and nine species, were caught during 212 longline sets. Catch rates were evaluated for the four most commonly occurring species, Atlantic sharpnose Rhizoprionodon terranovae, bonnethead Sphyrna tiburo, blacktip Carcharhinus limbatus and sandbar C. plumbeus sharks, as well as the aggregate catch rate of all sub-adult sharks. Neither lunar cycle nor tidal stage affected catch rates of any species other than blacktip sharks. In 2003, longline sets (n=80 sets) resulted in the capture of 177 sub-adult sharks from seven species. Overall catch rates were higher with squid than with spot, and bait type also affected shark species catch composition. Further, mean sizes of Atlantic sharpnose sharks were significantly different between the two bait types, indicating a possible ontogenetic shift in bait preference. For example, catch of neonate Atlantic sharpnose sharks was higher on hooks baited with squid than on hooks baited with spot, whereas catch of juveniles was higher on hooks baited with spot. Although timing of sampling did not influence catch rates of sub-adult sharks, bait choice could bias estimates of abundance for life certain stages and can affect the probability of detecting some species.